Walt Disney is a celebrity along with Mickey Mouse and Donald Duck. An image of Walt Disney has been superimposed over George Washington onto the U.S. dollar bill. This is not produced by Disney, it is a "celebrity note"
According to the Bureau of Engraving and Printing:
"A celebrity note is a note upon which the portraits of well-known personalities (such as Santa Claus and movie stars) are temporarily affixed. They, for the most part, are found to be genuine United States currency. Private businesses produce these novelty items by purchasing new currency notes from banks and subsequently apply the picture of a well-known personality over the engraved portrait on the note by means of a pressure-sensitive adhesive. These businesses then charge their customers premium prices. " (FAQ Library, "What is a Celebrity Note?", para 1)
"A determination of the legality of any particular celebrity note is a matter within the authority of the Department of Justice. The Bureau of Engraving and Printing's position regarding this matter is that this and similar other treatments of United States currency are demeaning. This type of enterprise is neither endorsed nor authorized by officials at the Bureau of Engraving and Printing." (FAQ Library, "What is a Celebrity Note?", para 4) (http://www.moneyfactory.gov/faqlibrary.html)